The long-term objective of this research is to determine how different types of luteal cells contribute to the activities, local regulation, and lifespan of the primate corpus luteum. Progress in this laboratory indicates that multiple subpopulations of nonhuman primate (macaque) luteal cells exist based upon functional and regulatory differences in progesterone production. Novel studies will test the theses that (1) subpopulations of macaque luteal cells differ in their use of lipoproteins as a cholesterol source for steroidogenesis, (2) luteal cell-cell interaction, analogous to the two-cell two-gonadotropin theory in the follicle, is required for estrogen production by the primate corpus luteum, (3) subpopulations of macaque luteal cells differ in their ability to produce inhibin-related peptides hibin, activin, subunits), and (4) different cell subpopulations and their activities as elucidated in vitro associated with the granulosa vs. theca luteal compartments of the macaque corpus luteum in situ. Collagenase-dispersed cells will be prepared from the corpus luteum of rhesus monkeys (Macaca mulatta) at midluteal phase of the menstrual cycle. Cell subpopulations win be separated by multiparameter flow cytometry, based on differences in light-scatter properties (a function of cell size and density) and the binding of fluorescent-tagged low density lipoprotein (LDL). Unsorted luteal cells and cell groups will be incubated in chemically-defined media containing various lipoproteins (high density lipoprotein, HDL; LDL; acetylated and oxidized LDL) and the steroidal precursors for the major x steroids, with or without gonadotropins luteinizing and follicle stimulating hormone, LH and FSH). 11 groups will be cultured separately and in combination to detect cell-cell interaction via physical contact or secreted precursors and factors. Synthesis and secretion of steroids and inhibin-related peptides will be assessed by biosynthetic labeling, radioimmunoassay and/or immunoblotting. Steroid enzymes d inhibin-related peptides in sorted cell groups and in sections of intact luteal tissue will be detected by immunocytochemistry. Unique information on the steroidogenic and peptidergic activities of cell subpopulations within the mate corpus luteum will be forthcoming. Elucidating the cellular origins, cell-cell interactions and regulation by endocrine and subsequently local factors should identify novel opportunities for controlling fertility and treating ovarian dysfunction in women.